The first version of Microsoft Windows hit the market in 1983. But unlike today's versions of Windows, Windows 1.0 was not an operating system (OS). It was a graphical user interface that worked with an existing OS called MS-DOS. Version 1.0 didn't look much like newer versions, either -- not even Windows 3.0, which many people think of as the first real version of Windows. Its graphics were simpler and used fewer colors than today's user interfaces, and its windows could not overlap.

Windows has changed considerably since then. In the last 20 years, Microsoft has released numerous full-fledged versions of the operating system. Sometimes, newer versions are significantly different from older ones, such as the change from Windows 3.1 to Windows 95. Other new releases have seemed more like enhancements or refinements of the older ones, such as the multiple consumer versions of the OS released from 1995 to 2001.

Microsoft's newest version of its operating system is Windows Vista. For many users, upgrading to Vista won't seem as dramatic as the upgrade from 3.1 to Windows 95. But Windows Vista has a number of new features, both in the parts that you can see and the parts that you can't.

At its core, Windows Vista is still an operating system. It has two primary behind-the-scenes jobs:

Managing hardware and software resources, including the processor, memory, storage and additional devices

Allowing programs to work with the computer's hardware

If all goes well, this work is usually invisible to the user, but it's essential to the computer's operation. You can learn about these tasks in more detail in How Operating Systems Work.

But when many people think of operating systems, they think of the portion they can see -- the graphical user interface (GUI). The GUI is what people use to interact with the hardware and software on the computer. In Windows systems, features like the Start menu, the recycle bin and the visual representations of files and folders are all part of the GUI.

Windows Vista's GUI is a 3-D interface called Windows Aero. Of the four editions of Windows Vista, three -- Home Premium, Business and Ultimate -- support Windows Aero. Home Basic, the most scaled-down edition of the OS, uses a less graphics-intensive GUI instead of Aero. The other editions can also use this basic GUI, so people with older computers that can't support lots of 3-D graphics can still upgrade to Vista.

We'll take a closer look at the Aero GUI and other Vista features next.

In addition to the four primary editions of Windows Vista, there are two editions for special markets. Windows Vista Enterprise is designed for very large businesses. Windows Vista Starter is a basic Vista OS for use in emerging markets, such as developing countries.